Reactance is defined as the imaginary part of Electrical impedance, and is analogous but not generally equal to the inverse of the susceptance.
However, for purely-reactive impedances (which are purely-susceptant admittances), the susceptance is equal to negative the inverse of the reactance.
In mathematical notation:

G=0⟺R=0⟺B=−1/X{\displaystyle G=0\iff R=0\iff B=-1/X}

Note the negation which is not present in the relationship between Electrical resistance and the analogue of conductance G, which = ℜ(Y){\displaystyle \Re (Y)}.

B=0⟺X=0⟺G=1/R{\displaystyle B=0\iff X=0\iff G=1/R}

The negation in one but not the other can be thought of as coming from the sign laws of sine and cosine, given the fact that conductance-analogue/resistance are the real parts and susceptance/reactance are the imaginary parts.